The International Building Code and ASCE 7 require a thorough geotechnical investigation before any structure rises in Savannah. ASTM D1586 governs the Standard Penetration Test, and in this city, the procedure faces a unique adversary: the Atlantic Coastal Plain. Beneath the live oaks and historic squares, the subsurface transitions rapidly from loose sands to stiff marl and Cooper Marl, often with groundwater within five feet of the surface. A routine SPT boring here tells a complex story. Our technical team runs the split-spoon sampler with a 140-pound hammer dropping 30 inches, recording blow counts every six inches. That raw data, combined with proper sampling technique, is what separates a foundation that settles predictably from one that cracks the brickwork on a Bull Street townhouse. For deeper profiling in soft zones, we often pair the SPT with a CPT test to catch thin clay seams the spoon might miss.
In coastal Georgia, an uncorrected N-value can be dangerously optimistic. We apply overburden and energy corrections to get the true soil behavior.
Method and coverage
Regional considerations
Savannah sits on unconsolidated Quaternary and Tertiary sediments that thicken toward the coast. The upper 20 to 40 feet often contain loose to medium-dense sands interbedded with soft clay lenses, a profile that demands rigorous liquefaction screening under ASCE 7-22. During the 1886 Charleston earthquake, ground failure and sand blows were reported as far south as the Savannah River basin, and modern probabilistic maps place the area in a moderate seismic hazard zone. A single inaccurate N-value in a loose sand at 15 feet can flip a liquefaction analysis from 'low risk' to 'high risk,' triggering costly ground improvement. Our reports provide the corrected N1(60) values needed for the simplified procedure by Youd and Idriss, giving the structural engineer a defensible basis for either ruling out liquefaction or designing mitigation like stone columns or deep foundations.
Process video
Standards that apply
ASTM D1586-18: Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils, ASTM D2487-17: Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), ASCE 7-22: Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Chapter 20 (Seismic Site Classification), International Building Code (IBC) 2021, Section 1803: Geotechnical Investigations
Complementary services
SPT Drilling and Sampling
Truck-mounted or limited-access boring rigs advancing hollow-stem augers or mud rotary through coastal plain soils. We record N-values, retrieve split-spoon samples, and log the stratigraphy with a field geologist present for every boring.
Laboratory Testing and Reporting
Classification tests (grain size and Atterberg limits) on selected SPT samples, plus correlation of N-values with strength and compressibility. The final report includes boring logs, site class per ASCE 7, and foundation recommendations for shallow or deep systems.
Typical parameters
Q&A
How much does an SPT boring cost in Savannah?
For a standard SPT boring within the Savannah metro area, budget between US$470 and US$650 per boring, assuming access for a truck-mounted rig. The final cost depends on depth, mobilization distance, and the number of borings on the site. A single deep boring to 50 feet will be at the higher end, while a multi-boring program on a clear lot may trend lower per hole.
What depth do you typically drill for a residential foundation investigation?
For a single-family home or townhouse in Savannah, we generally advance SPT borings to a minimum depth of 25 to 30 feet, or until we encounter competent bearing material with consistent N-values above 15. If the structure includes a basement or if we find soft organic silts in the upper profile, we extend the boring deeper to evaluate the thickness of the compressible layer and confirm the depth to the Cooper Marl where present.
How do you handle the high groundwater table during SPT sampling?
Savannah's shallow groundwater, often within three to five feet of the surface, requires mud rotary or hollow-stem auger techniques to keep the borehole open. We use drilling mud or continuous auger flights to balance hydrostatic pressure and prevent sand heave into the casing. Without this, the SPT can produce artificially low blow counts in loose saturated sands, which would compromise liquefaction assessments and settlement calculations.